Protective means for electron discharge devices



c. v. LrrToN 2,477,633

PROTECTIVEMEANS FOR ELECTRON DISCHARGE DEVICES Aug. 2, 1949.

Filed NOV. l, 1945 INVENTOR CHA/PL f5 van IIIII lATTORNEY atenteci Allg. 2, 1949 "'RG'EECTAIV'EMEANS EORAELEGTRON" .DISGHARGE DEVIIGES Y titanes. v, Liften; Redactar city; cani'. appiieauunfNo-vemberi, 19451,V` serial-Nm 62eme1 This invention relatesftorn .Inagnetronsj or :similar electron` discharge tulcnesv and.; in particular to magnetrons of the cavity resonator ,ty-pe. wherein the cavities' are coupled` to the loadcirc-uit throughian impedanceA tr,ansfor-mer-andv a Wavel guide.

In magnetrons of the above type it-isconventionalv to extract -thetgeneratedliigh frequency energy from the: magnetron cavities at. a pointof.y maximum, current density and; minimum .potential,i. e.,4 alpointof lowimpedance.4 `A-,rec-

tangularl wave guide operatingongthe TEiio-mode (which is conventional in applications o f this type) has a ratio of electric` tofmagneticeldintensities which is much greater than theratio of like fieldsat-the poi-nt oflow impedance the magnetron cavities; I-t--is thereforefdesirable to coupletle'wave guidetothe magnetroncavities through` an` impedance; matching. trans--v former to avoidreiiections ofi` the'. trai'ismitted4 wave.

The impedance-- matching:Y transformen is preferably ofv the formaofiV a divergfing. line ,Whosefimf pedanceV varies.- substa-ntially exponentiallyfromA its low impedance `to` its-high impedance, l,enda- T-he transformer isfA contained inf an evacuated horn. shaped member Whichisfstructurallgt parte Aa-lass or other-- in sulating;

of. the magnetron. window separateathe-Lvacuous spacefof thema-grnetron` from theV nonvacuous space of; tnavvave;v

guide.

Ithas beenfound thatfinfthe operationioi the magnetron f there isa :tendency for freeelectrcris:A to escape fromthev magnetron rescna'ting-.,cav# ities and. to-be projected at highvelocityfmf ahypocycloidal motion through the impedance transforming-member-itoward the,-1insulatingfWin--u dow.` Should i thesefie-lectronsl strike ting-Window;l intense` local i heating; of the'Wirlidowv occurs;v tree' sulting in suck-in and damage to then-1an,-

netronp. Itl isLJa'lsc') possiol'e that the heating of the Window may be due, in part at least, to positive ions produced'lby tHe-impacte of electrons against gas molecules in` their travel toward-the Window. l

In accordance with my invention I "provide a magnetic fieldacross@tneivacucsspabe of the hornishaped member, saidfield havingeaMdi-f rection which is substantia-lly.;` perpendicular.' to the motion of the electrons. This magnetichfield causes the electrons to follow a path which curves away from the Window and to strike harmlessly against the walls of the horn-shaped member.

It is the lprimary object of my invention to prevent the aforesaid bombardment of the insu- 3 tuning means comprises a C-ring 9. Both the L- ring and C-ring are described in my application Serial Number 626,131, entitled Reactance tuning device filed November 1, 1945, in which the C-ring structure is specically claimed.

Referring now to that part of the magnetron to which my present invention is directed, and to both Figs. 1 and 2, an evacuated horn-shaped member I0 is positioned between the body I and a wave guide Il. The wave guide may be of considerable length so only that portion which is adjacent the horn-shaped member is illustrated in the drawing. A load circuit, n'otshown, is connected to the other end of the wave guide. The construction of a wave guide for a particular frequency or for a small range of frequencies is weil known in the art and adescription thereof is therefore unnecessary. The member l0 is closed at its enlarged end by a closure member I2, vthe two members being welded together around the periphery of suitable flanges which are iormed integrally with the members.

A glass or other type of non-conducting window I3' is sealed over an opening in the closure member IZ. This permits the magnetron to be evacuated while at the same time allows the wave energy developed in the cavities of the magnetron to pass from the horn or transformer lu into the wave guide. The window is preferably of sioned that at approximately the mean frequency to which the magnetron may be tuned it represents a substantially infinite or at least avery high impedance across the Wave guide and therefore does not materially iniluence the operation n of the system.

Within themember I0 are two ramps I4 and I5, the surfaces of which diverge exponentially and constitute a transmission line of gradually increasing impedance between the cavities of the magnetron and the wave guide. The impedance of the line adjacent the resonant cavities of the magnetron is low and substantially matches the impedance of the cavities. The impedance of the line at its outer end is such that it substantially matches the impedance of the wave guide I I. It will be observed that the dimensions of the open end of the horn and` of the wave guide are substantially the same. This permits a gradual change of impedance between these two members inasmuch as surfaces of the ramps are widely spaced at this point.

Asaforesaid it has been found that during magnetron operation there are occasions when free electrons escape from the cavity ofthe magnetron to the space within the horn l0. If these electrons strike the window with sufficient velocity the window becomes softened by overheating and failure due to suck-in will occur. In order to prevent such failure, two magnetic shoes I6 and III are positioned one on each side of the horn as shown in Fig. 1. The magnetron shoes are energized from the eld coils I8 and I9 which also supply the magnetic eld for the operation of the magnetron as is well understood. The magnetic shoes are so positioned with respect to the horn that a deiiecting field is produced across the shoes substantially at right angles to the path of the free electrons. The field deflects the electrons causing them to impinge on the inner surface of the horn where their energy is harmlessly dissipated.

an elliptical shape and so dimen- Iii Although I have illustrated only a single enibodiment of my invention, other modifications will be apparent to one skilled in the art and it is my intention that the scope of my invention be limited only by the objects thereof and the appended claims. For example, the magnetic shoes for delecting the electrons could be permanent magnets suitably associated with the evacuated horn shaped member, or an electromagnetic eld could be produced by suitably energized coils distinct from the field coils I8 and I9.

What is claimed is:

l. Protective means for the output coupling means for a magnetron with eld poles used as a source of electromagnetic waves and undesired stray electrons, said magnetron including an evacuated member and insulating window closing one end of said member, said Waves travelling through said window, said protective means comprising electromagnetic means mounted adjacent said evacuated member for producing a magnetic field transverse to the direction of travel of said waves through said window and energizing means f, associated with said electromagnetic means for causing stray electrons to be deflected away from said Window.

2. The combination claimed in claim 1 wherein said means for producing said magneto field comprises a pair of magnetic shoes disposed exterior to and on opposite sides of said evacuated member, said magnetic shoes being positioned to be magnetically connected to the eld of the poles of said magnetron,

3. Protective means for the output coupling means oi a magnetron which includes eld poles, an evacuated envelope, a plurality of cavity resonators mounted therein, an impedance transformer coupled at one end to one of said resonators and having a window at the opposite end through which electromagnetic waves from said resonators travel, and divergent ramps mounted in said transformer in a plane parallel to the direction of travel of said waves, said protective means comprising electromagnetic means mounted adjacent said transformer for producing a magnetic eld transverse to the direction of travel of said waves through said window and energizing means associated with said electromagnetic means for causing stray electrons to be deflected away from said window.

4'. Protective means according to claim 3 in which said means for producing said magnetic field comprises a pair of magnetic shoes fitting closely about said impedance transformer and mounted closely adjacent thereto and on opposite sides of the plane containing said ramps and means for magnetically connecting said magnetic shoes to the field poles of said magnetron.

CHARLES V. LITTON.

REFERENCES CITED The following referenlces are of record in the 

